1. Field of the Invention
The present invention relates to a motor-driven, rotatable chuck for an annular core bit for working brittle materials, such as stone, concrete or masonry.
2. Description of the Prior Art
During working of brittle materials with a rotatable annular core bit formed of a cylindrical tube provided at its end surface with grinding or cutting members and having a diameter, usually, of more than 100 mm, high torques and axial forces are transmitted from a chuck to the bit through a shank end of the bit having a diameter, usually, of less than 50 mm, e.g., with an inner thread of 1¼″
With simple chucks having a rotatable spindle with a threaded support and an axial stop flange, which are only discussed here, high torques and high axial forces lead to frictional bonding of the shank end in the chuck. As a result, replacement of an annular core bit is usually rather cumbersome, time-consuming, and is possible only with a special mounting tool. Despite these drawbacks, the market for such chucks for annular core bits expands.
According to U.S. Pat. No. 4,911,253, European Publication EP-253581, and German Utility Model DE-299 18 965 U1, a motor-driven chuck for an annular core bit/annular core bit adapter has a threaded support and an axial stop flange. For releasing the frictional bond between the axial stop flange and the threaded support of the chuck and the jammed annular core bit/annular core bit adapter, a wrench adapted to the hexagon of the shank end of the annular core bit/annular core bit adapter is required.
A quick-action coupling for a tool-free replacement of an annular core bit, which is disclosed in DE-299 18 965 U1, is not suitable for chucks having a threaded support.
German Patent DE-38 24 040 C1 discloses a locking device formed as a barrel nut for a stop member which is arranged between the nut and a working tool mountable on al threaded support with an axial stop flange and at the working tool side of the axial stop flange. The axial stop member is axially displaceable, within narrow limits, and is pressed axially against the barrel nut by locking wedge means displaceable within narrow limits. The locking wedge means are released with a manually actuated, displaceable release member. DE-38 24 040 C1 discloses a locking device for a disc-shaped working tool and is not suitable for an annular core bit with an inner thread.
An object of the invention is a chuck with a threaded support and an axial stop flange and which would enable an easy replacement of an annular core bit with an inner thread.